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Built into Windows 10 and 11, Microsoft Defender is the most consistently reliable antivirus suite around. It got perfect 100% protection scores in both AV-Test and SE Labs’ most recent tests.

Core anti-malware components include real-time protection and on-demand scans covering everything from quickly checking a folder to a comprehensive offline scan that checks for hard-to-remove threats such as rootkits by scanning the system without booting into Windows. However, scheduled scans have to be set up via Windows Task Scheduler.

As well as virus protection, Defender includes ubiquitous Windows Firewall, parental controls and remote management of your family’s devices, reputation-based site blocking in Edge and application blocking in general, system health reports, and the ability to disable all notifications.

Although Microsoft Defender is incredibly good, you’ll need an alternative such as Avast or Bitdefender’s free antivirus if you’re running an older version of Windows.

Reviewer: K.G. Orphanides
Full review: Microsoft Defender Antivirus review

Partly supported by advertising and partner promotion, Avast Free Antivirus includes core protection modules against malware via web, file, network and mail, as well as ransomware defence for your choice of critical folders. 

It carries out real-time scanning of potential threats, as well as on-demand and scheduled system scans, and features a do not disturb mode to eliminate interruptions of fullscreen applications.

Avast’s malware detection engine got perfect scores in AV-Test’s latest real-world exposure and reference file scanning tests, with a six-out-of-six system performance racing and only two false positives. It blocked 99.9% of malicious content in AV-Comparatives’ real-world protection tests, with 20 false positives, and achieved a perfect accuracy rating in the most recent tests by SE Labs.

It’s no more accurate than Microsoft Defender, so Windows 10 and 11 users should stick to that, but is a solid choice for older Windows PCs.

Reviewer: K.G. Orphanides
Full review: Avast Free Antivirus

Bitdefender Antivirus Free Edition shares its detection engine with the company’s paid-for editions, but provides an otherwise bare-bones experience.

Bitdefender’s engine typically performs well in tests. It achieved a 100% detection rating in AV-Test’s real-world and reference scanning tests, with only a single false positive and a 99.9% rating with three false positives in AV-Comparatives’ most recent real-world protection test. The software was not included in SE Labs’ recent tests.

Bitdefender’s interface is refreshingly free of clutter. There’s just a single, compact status screen, showing your protection status. Here, you can activate a system scan or drag and drop in any file or folder to immediately check it for threats. However, you can’t schedule scans and there’s no dedicated ransomware defence module.

The app includes malicious site filtering, phishing and fraud protection for the web, and allows you to disable notifications. You also get limited remote device management of up to 25 installations of Bitdefender free

It can’t quite match Microsoft Defender’s outstanding performance if you’re running Windows 10 or 11 systems. However, it’s a great choice if you’re still using Windows 7 or 8.1 and want a truly simple interface to work with and a minimum of bother. 

Reviewer: K.G. Orphanides
Full review: Bitdefender Antivirus Free Edition

Bought by rival Avast in 2016, AVG’s anti-malware suites use the same detection engine as its stablemate, but with a different interface and a slightly different range of integrated tools.

AVG Free Antivirus has a more limited feature set than its paid-for counterparts, but the essential real-time and file-scanning anti-malware components are there, along with on-demand and scheduled scans, browser and email scanning components, and an anti-ransomware tool that blocks unauthorised programs from making changes to selected directories.

AVG’s detection engine performed identically to Avast’s in recent tests by AV-Test, AV-Comparatives and SE Labs. Both detected and protected against 100% of malware in AV-Test and SE Labs’s tests, and 99.9% of malware in tests by AV-Comparatives. However, AV-Test’s data shows that AVG has a greater impact on performance.

AVG is a long-standing public favourite among free anti-malware tools and continues to do the job reasonably efficiently. However, it’s no more effective than Microsoft Defender, which comes pre-installed on Windows 10.

Reviewer: K.G. Orphanides
Full review: AVG Free Antivirus

Avira has a longstanding reputation as a lightweight antivirus suite that’ll run on almost anything. Unfortunately, its performance in the most recent tests by AV-Test and AV-Comparatives (although by no means ineffective against the latest malware) wasn’t quite up to most of its rivals. Avira Free Security was the worst performer across two months of AV-Test’s real-world tests, scoring 99.2% and 99.9% respectively. 

It protected the test system in 98.9% of AV-Comparatives’ test exposures, although it scored a perfect 100% across all protection and accuracy metrics in SE Labs’ latest tests.

Free users only get access to the Real-time protection module, plus scheduled and on-demand scans. If you want the dedicated web, email and ransomware protection modules, you’ll be prompted to subscribe to Avira Prime. Similarly, the free version has no do-not-disturb mode for gaming.

It comes with plenty of other tools for system optimisation, file shredding, and tweaking Windows’ privacy settings, plus a very limited 500MB/month VPN allowance. These are all handy, but can’t quite outshine Windows Defender for Windows 10 and 11 users.

Reviewer: K.G. Orphanides
Full review: Avira Free Security